Fig. 2.

Time course of postnatal changes in expression of major serotoninergic and other related receptors in orofacial and spinal motoneurons. The diagrams summarize data for selected orofacial and spinal motoneurons. Since the results from different sources used different scales and units of measure, we normalized published results relative to the highest value in each study. The data used to compile the diagram were derived from: Reference (Ref.) #1 - proportion of XII motoneurons expressing 5-HT_1A, 5-HT_1B and 5-HT_2A receptor mRNA, and 5-HT_2A receptor immunohistochemistry in XII and upper cervical motoneurons (Volgin et al., 2003); Ref. #2 − 5-HT_1A receptor mRNA and 5-HT_1A and thyrotropin releasing hormone receptor binding in the XII nucleus (Bayliss et al., 1997); Ref. 3 − 5-HT_1B receptor immunohistochemistry (Berger and Huynh, 2002). Of general note here are three points: (1) the time course of expression differs among distinct receptor subtypes for the same neurotransmitter even within a single motoneuronal pool (e.g., 5-HT_1A, 5-HT_1B and 5-HT_2A receptors in XII motoneurons); (2) the same receptor can follow different developmental time courses in orofacial (XII) and spinal motoneurons (e.g., 5-HT_2A receptors in the XII nucleus and cervical ventral horn); and (3) some receptors can exhibit very large and biphasic changes, at least at the mRNA level, within just a few days (e.g., 5-HT_1B receptor mRNA in XII motoneurons).